I. Field of the Invention
This invention relates to rotary drilling heads incorporating a kelly drive and stripper rubbers for developing a well and, in particular, to a hydraulically actuated clamp assembly of the drilling head which can be remotely operated to permit access to the interior components of the drilling head.
II. Description of the Prior Art
A rotary drilling head is typically attached to the top of a well casing to facilitate drilling operations while providing safety features and drilling mud diversion. The drilling apparatus generally comprises a rotatable drill stem used to rotate a drill bit within the well. The drill stem may include a string of drill pipes connected to a non-circular pipe, commonly referred to as a kelly, slidably extending through the rotary table. The kelly transmits the drive from the rotary table to the drilling head via the kelly bushings. In the usual forward circulation drilling operation, a drilling fluid may be forced through the interior of the hollow drill stem and drill bit of the bottom of the hole. Cuttings and debris at the bottom of the well are carried upwardly in the annulus between the outside of the drill string and the well bore. The drilling head includes a stationary outer housing or spool which is secured to the top of the casing, a drive ring and bearing assembly, and a drive assembly in cooperation with the drive ring and bearing assembly. The drive assembly includes a kelly bushing. A rubber stripper is attached for rotation with the drive ring in slidable sealing engagement with the kelly drive.
In operation, the split kelly bushing is slidably connected to the kelly drive. As the kelly drive is lowered through the drilling head the kelly bushing is received within the drive assembly. Rotation of the kelly causes the kelly bushing to rotate which rotates the drive assembly which in turn rotates the drive ring and attached rubber stripper. The rubber stripper diverts the drilling mud through a side port of the drilling head while maintaining sealing engagement with the kelly.
Various arrangements have been provided for removing worn drilling head components from within the spool. Early drilling heads incorporated an expandable/contractible split clamp to secure the upper assembly of the drilling head to the spool. Such clamps utilize a plurality of pivoting segment which together may be moved radially outward or inward. Typically, such clamps are manually operated and therefore required a workman to go under the rig floor, a precarious position. Hydraulically operated clamps were later developed, however, these clamp assemblies tend to accumulate mud and debris obstructing radial movement. Other clamp configurations also have proven unsatisfactory in allowing remote unclamping of the drilling head for access to the interior components.